Method for performing a charge exchange in an internal combustion engine

ABSTRACT

A method and system for perform a charge exchange in internal combustion engine comprising an additional intake and exhaust valve lifts performed during positive pressure gradients between the intake and exhaust systems to reducing scavenging losses and increase torque during low engine speeds.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German Patent Application No.102014205414.1, filed Mar. 24, 2014, the entire contents of which arehereby incorporated by reference for all purposes.

FIELD

The present disclosure relates a method and system of performing acharge exchange in an internal combustion engine.

BACKGROUND SUMMARY

Engines may use a turbocharger or a supercharger to improve enginetorque/power output density and minimize fuel consumption. In oneexample, a turbocharger may include a compressor and a turbine connectedby a drive shaft, where the turbine is coupled to an exhaust manifoldside and the compressor is coupled to an intake manifold side. However,such a supercharged or turbocharged engine, under low engine speedconditions, may experience torque drop due to a decrease in exhaust-gasmass flow which may subsequently lower a turbine pressure ratio.

One approach to address the issue of torque drop under low engine speedconditions has been to vary valve overlap through variable valve timing,for example. Another approach has been to use an exhaust-gasturbocharger with a small turbine cross-section or by the use ofmultiple exhaust-gas turbochargers.

The inventors herein have recognized various issues with the abovesystems. For example, scavenging losses may occur during valve overlap,which may prevent a full charge of fresh air from entering the cylinderand participating in combustion, thus reducing power output. Moreover,the large valve overlap needed to overcome torque deficit at low enginespeeds may not be viable in internal combustion engines with highcompression ratios, such as diesel engines, due to the proximity of thepiston to the valves as it moves toward top dead center. An exhaust-gasturbocharger with a smaller cross-section may be able to generate chargepressure at low exhaust-gas flow rates, but may consequently shift thetorque drop further toward lower engine speeds.

One approach that at least partially addresses the above issues is amethod and a system, comprising opening at least one exhaust valve tomaximum valve lift during a charge exchange of a combustion chambercomprising a piston, actuating at least one intake valve before thepiston reaches top dead center of the combustion chamber during thecharge exchange to perform an additional intake valve lift such that anintake pressure is greater than an exhaust pressure, then opening atleast one inlet valve to maximum valve lift during the course of chargeexchange and actuating at least one exhaust valve before the pistonreaches bottom dead center during charge exchange to perform anadditional exhaust valve lift such that intake pressure is greater thanexhaust pressure. In this way, the additional valve lifts may reducescavenging and/or may provide increased low end torque withoutincreasing exhaust gas temperature, in one example.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an example vehicle system.

FIG. 2A shows, in a diagram, the valve lift curves h_(intake),h_(exhaust) of an inlet valve and of an outlet valve.

FIG. 2B shows, in a diagram, the valve lift curves hintake, hexhaust ofan inlet valve and of an outlet valve.

FIG. 3 shows an example method flowchart of the additional valve lifts.

FIG. 4 shows an example operating routine for the additional valve liftsystem.

DETAILED DESCRIPTION

The present application relates to a system for performing a chargeexchange in an internal combustion engine comprising at least onecylinder head with at least one cylinder, each cylinder comprising atleast one inlet opening for the supply of fresh air via an intake systemand comprising at least one outlet opening for discharging the exhaustgases via an exhaust-gas discharge system and comprising a piston whichis movable along a piston longitudinal axis between a bottom dead centerand a top dead center, and at least two valve drives with at least twovalves which are movable along their longitudinal axis between a valveclosed position and a valve open position, performing a maximum valvelift, in order to open up and block the at least one inlet opening andthe at least one outlet opening of the at least one cylinder during thecourse of a charge exchange, and having at least two actuating devicesfor opening the valves counter to a preload force.

An internal combustion engine of the above-stated type is used as adrive for motor vehicles. Within the context of the present application,the expression “internal combustion engine” encompasses Otto-cycleengines, diesel engines and also hybrid internal combustion engines,which utilize a hybrid combustion process, and hybrid drives whichcomprise not only the internal combustion engine but also an electricmachine which can be connected in terms of drive to the internalcombustion engine and which receives power from the internal combustionengine or which, as a switchable auxiliary drive, additionally outputspower.

Internal combustion engines have a cylinder block and at least onecylinder head which are connected to one another to form at least onecylinder. To hold the pistons or the cylinder liners, the cylinder blockhas a corresponding number of cylinder bores. The cylinder headconventionally serves to hold the valve drive. To control the chargeexchange, an internal combustion engine requires control elements andactuating devices for actuating the control elements. During the chargeexchange of a cylinder, the combustion gases may be discharged via atleast one outlet opening and the charging of the combustion chamber,that is to say the induction of the fresh air, takes place via at leastone inlet opening. To control the charge exchange, in four-strokeengines, use may be made almost exclusively of lifting valves as controlelements, which lifting valves perform an oscillating lifting movementalong their longitudinal axis during the operation of the internalcombustion engine and which lifting valves open and close the inlet andoutlet openings in this way. The actuating device required for themovement of a valve, including the valve itself, is referred to as thevalve drive.

It is the object of the valve drive to open and close the at least oneinlet and/or outlet opening of a cylinder at the correct times, with afast opening of the largest possible flow cross sections being sought inorder to keep the throttling losses in the inflowing and outflowing gasflows low and in order to better enable the best possible charging ofthe cylinder and a complete discharge of the exhaust gases. Accordingsome approaches, therefore, a cylinder is also often and increasinglyprovided with two or more inlet and outlet openings.

According to some approaches, the intake lines which lead to the inletopenings, and the exhaust lines which adjoin the outlet openings, may beat least partially integrated in the cylinder head.

A primary aim in the development of internal combustion engines is thatof minimizing fuel consumption. In this connection, too, thesupercharging of internal combustion engines is becoming ever moreimportant. Supercharging may be a suitable means for increasing thepower of an internal combustion engine while maintaining an unchangedswept volume, or for reducing the swept volume while maintaining thesame power. For the same vehicle boundary conditions, it is thuspossible to shift the load collective toward higher loads, at which thespecific fuel consumption may be lower. Supercharging of an internalcombustion engine consequently assists in the efforts to minimize fuelconsumption, that is to say to improve the efficiency of the internalcombustion engine.

The configuration of the exhaust-gas turbocharging often posesdifficulties, wherein it is basically sought to obtain a noticeableperformance increase in all engine speed ranges. According to someapproaches, however, a torque drop may be observed in the event of acertain engine speed being undershot. Said torque drop is understandableif one takes into consideration that the charge pressure ratio isdependent on the turbine pressure ratio. For example, if the enginespeed is reduced, this leads to a smaller exhaust-gas mass flow andtherefore to a lower turbine pressure ratio. This has the result that,toward lower engine speeds, the charge pressure ratio and the chargepressure likewise decrease, which equates to a torque drop.

The drop in charge pressure can basically be counteracted through theuse of a small exhaust-gas turbocharger, that is to say an exhaust-gasturbocharger with a small turbine cross section, in order to be able togenerate an adequate charge pressure even at low exhaust-gas flow rates.This will however ultimately only shift the torque drop further towardlower engine speeds. Furthermore, said approach, that is to say thereduction in size of the turbine cross section, is subject to limitsbecause the desired supercharging and performance increase should bepossible without restriction and to the desired extent even at highengine speeds.

According to some approaches, it has been sought to improve the torquecharacteristic of a supercharged internal combustion engine by variousmeasures, for example by means of a small design of the turbine crosssection in combination with exhaust-gas blow-off, or the use of multipleexhaust-gas turbochargers.

The torque characteristic may also be advantageously influenced by meansof multiple exhaust-gas turbochargers connected in series. By connectingtwo exhaust-gas turbochargers in series, of which one exhaust-gasturbocharger serves as a high-pressure stage and one exhaust-gasturbocharger serves as a low-pressure stage, the engine characteristicmap can advantageously be expanded, specifically both in the directionof smaller compressor flows and also in the direction of largercompressor flows.

For example, with the exhaust-gas turbocharger which serves as ahigh-pressure stage, it is possible for the surge limit to be shifted inthe direction of smaller compressor flows, as a result of which highcharge pressure ratios can be obtained even with small compressor flows,which considerably improves the torque characteristic in the lowerengine speed range. This is achieved by designing the high-pressureturbine for small exhaust-gas mass flows and by providing a bypass lineby means of which, with increasing exhaust-gas mass flow, an increasingamount of exhaust gas is conducted past the high-pressure turbine. Forthis purpose, the bypass line branches off from the exhaust-gasdischarge system upstream of the high-pressure turbine and opens intothe exhaust-gas discharge system again upstream of the low-pressureturbine, wherein a shut-off element is arranged in the bypass line inorder to control the exhaust-gas flow conducted past the high-pressureturbine.

The response behavior of an internal combustion engine supercharged inthis way is considerably improved in relation to a similar internalcombustion engine with single-stage supercharging, because therelatively small high-pressure stage is less inert, that is to say therotor of a smaller-dimensioned exhaust-gas turbocharger can beaccelerated more rapidly.

The torque characteristic of a supercharged internal combustion enginemay furthermore be improved by means of multiple turbochargers arrangedin parallel, that is to say by means of multiple turbines of relativelysmall cross section arranged in parallel, wherein turbines may beactivated successively with increasing exhaust-gas flow rate.

The torque characteristic of a supercharged internal combustion enginemay also be improved by virtue of the at least one exhaust-gasturbocharger being supplemented by a mechanical charger, for example acompressor.

In addition to a conceptual improvement of the exhaust-gas turbochargingarrangement as described above, some approaches also include methods forimproving the torque characteristic of an exhaust-gas-turbochargedinternal combustion engine, the aim of which methods is to increasetorque, and to overcome the torque deficit at low engine speeds, forexample. Here, a basic cause of the torque deficit at low engine speedsis considered to be the excessively low exhaust-gas flow rate at lowengine speeds.

By means of variable valve control, the valve overlap, that is to saythe crank angle range in which the outlet is not yet closed while theinlet is open, can be varied. During the valve overlap, scavenginglosses can occur, wherein some of the inducted fresh air flows throughthe cylinder without participating in the subsequent combustion.Variable valve control permits a variation of the valve overlap in amanner dependent, inter alia, on the engine speed.

In the case of the exhaust-gas-turbocharged applied-ignition internalcombustion engines, at low engine speeds, a large valve overlap issuitable for considerably raising the maximum torque and improvingtransient operating behavior. A pressure gradient that exists betweenthe inlet side and outlet side at low engine speeds assists an effectivescavenging process of the cylinders with fresh air and better enables agreater cylinder charge and thus higher power.

In the case of Otto-cycle engines with a relatively low compressionratio of, for example, ε≈10 for naturally aspirated engines or ε≠8 . . .9 for supercharged engines, the torque deficit at low engine speeds maybe counteracted with a large valve overlap. In the case of internalcombustion engines with high compression ratio, such as for examplediesel engines, a large valve overlap often cannot be implementedbecause the piston, as it passes through top dead center, comes veryclose to the inlet valves and/or the outlet valves, and opening of thevalves in the context of a valve overlap is not possible to anunrestricted extent.

Against the background of that stated above, it is the object of thepresent application to specify a method according to the preamble ofclaim 1 by means of which the torque deficit at low engine speeds can becounteracted and the torque characteristic, in particular of anexhaust-gas-turbocharged internal combustion engine, can be improved.

Said object may be achieved by means of a method for performing a chargeexchange in an internal combustion engine comprising at least onecylinder head with at least one cylinder, each cylinder comprising atleast one inlet opening for the supply of fresh air via an intake systemand at least one outlet opening for discharging the exhaust gases via anexhaust-gas discharge system and a piston which is movable along apiston longitudinal axis between a bottom dead center and a top deadcenter, and at least two valve drives with at least two valves which aremovable along their longitudinal axis between a valve closed positionand a valve open position, performing a maximum valve lift, in order toopen up and block the at least one inlet opening and the at least oneoutlet opening of the at least one cylinder during the course of acharge exchange, and having at least two actuating devices for openingthe valves counter to a preload force, wherein the inlet valve of the atleast one inlet opening is actuated in such a way that said inlet valveperforms an additional valve lift before the piston, during the courseof the charge exchange, reaches top dead center and before the inletvalve, during the course of the charge exchange, performs the maximumvalve lift.

According to the application, the inlet valve of the at least one inletopening performs at least two valve lifts, wherein the main, relativelylarge valve lift, which serves primarily for the charge exchange, ispreceded by an additional, relatively small valve lift.

The additional, relatively small valve lift serves for the scavenging ofresidual gas out of the cylinder. The scavenging of residual gas isassisted by virtue of the piston moving toward top dead center, passingthrough top dead center or being situated in the vicinity of top deadcenter shortly before top dead center, such that the combustion chambervolume present as the additional valve lift is performed is relativelysmall or is only insignificantly larger than the compression volume whenthe piston is at top dead center.

The extensive scavenging of the residual gas better enables the greatestpossible cylinder fresh charge in the next working cycle and thus agreater energy yield in the subsequent combustion cycle, that is to sayan increase in power and thus increase in torque at the same, inparticular at a lower, engine speed.

In the case of exhaust-gas-turbocharged internal combustion engines, thescavenging process also has a further advantageous effect, specificallythe effect that the turbine, arranged in the exhaust-gas dischargesystem, of an exhaust-gas turbocharger is provided with a greater massflow. The greater mass flow through the turbine yields a higher turbinepressure ratio, a higher charge pressure ratio and thus, at the inletside, a higher charge pressure, which likewise contributes to improvedcharging of the cylinder, that is to say to the greatest possiblecylinder fresh charge in the next working cycle. This effect, too, leadsto an increase in power, that is to say to an increase in torque at aconstant engine speed.

The fresh air that is introduced into and/or conducted through thecylinder during the scavenging of residual gas is furthermore heatedowing to convection as it flows over the piston crown and over the hotcombustion chamber internal walls, such that the mass flow introducedinto the exhaust-gas discharge system is at a higher temperature andthus has increased enthalpy. Furthermore, the hot scavenged residual gasfurther contributes to increasing the enthalpy of the mass flow that issupplied to the turbine. Aside from the increase in mass flow, theincrease in enthalpy—as described above—also leads to a higher chargepressure and thus to an increase in torque.

Whereas, in the case of a relatively large valve overlap in which theinlet valve must be opened earlier and/or the outlet valve must beclosed later, there is the risk of the piston, as it travels through topdead center, coming into contact with an open inlet valve and/or an openoutlet valve, the additional lift according to the present applicationcan be performed before top dead center is reached and with a spacing totop dead center, without the piston making contact with, and damaging,the open inlet valve.

The method according to the present application achieves the object onwhich the present application is based, specifically that of specifyinga method by means of which the torque deficit at low engine speeds canbe counteracted and the torque characteristic, in particular of anexhaust-gas-turbocharged internal combustion engine, can be improved.

Further advantageous embodiments of the method according to the presentapplication will be explained in conjunction with the subclaims.

Embodiments of the method may be advantageous in which the inlet valveof the at least one inlet opening is actuated, for the purpose ofperforming the additional valve lift, while at least one outlet openingof the at least one cylinder is at least temporarily open. The fresh airthat is introduced via the inlet opening during the course of theadditional valve lift can, in the present case, flow unhindered throughthe cylinder and exit the cylinder via the outlet opening, whereby thescavenging process is advantageously assisted.

Embodiments of the method may be advantageous in which the inlet valveof the at least one inlet opening is actuated, for the purpose ofperforming the additional valve lift, only when a pressure gradientprevails which is such that the pressure in the intake system is higherthan the pressure in the exhaust-gas discharge system.

A pressure gradient between the intake system and the exhaust-gasdischarge system assists the scavenging process with fresh air, that isto say effective scavenging of the cylinder. In this connection, it mustbe taken into consideration that, owing to the intermittent chargeexchange, gas-dynamic wave phenomena occur in the intake system and inthe exhaust-gas discharge system, as a result of which the pressure atthe inlet side and at the outlet side generally changes with time.

Embodiments of the method may be advantageous in which the additionalvalve lift of the inlet valve is performed up until 50° CA before topdead center.

Embodiments of the method may be advantageous in which the additionalvalve lift of the inlet valve is performed up until 30° CA before topdead center.

The closer to top dead center the additional valve lift is performed,the smaller is the present combustion chamber volume as the additionalvalve lift is carried out, and the more effective or pronounced is thescavenging process and/or the temperature increase of the scavenging airas it flows over the combustion chamber internal walls, for example overthe piston crown. Both assist in increasing the torque, for example atlow engine speeds. The crank angle point at which the additional valvelift is performed must be coordinated with the magnitude of theadditional valve lift.

Embodiments of the method may be advantageous in which the inlet valveof the at least one inlet opening is, after performing the additionalvalve lift, moved into the closed position again before said inlet valveis opened again for the purpose of performing the maximum valve liftduring the course of the charge exchange.

Embodiments of the method may however also be advantageous in which theinlet valve of the at least one inlet opening, after performing theadditional valve lift, is not moved into the closed position but isopened further for the purpose of performing the maximum valve liftduring the course of the charge exchange.

It may be the case that there is no time available for the inlet valveto be moved into the closed position after performing the additionalvalve lift, because said inlet valve must immediately be opened widelyand fully for the purposes of the charge exchange. This may be the casefor example if the additional valve lift is performed very close to topdead center.

In this connection, however, embodiments of the method may beadvantageous in which the inlet valve of the at least one inlet opening,after performing the additional valve lift, is moved in the direction ofthe closed position in order to reduce the valve lift by up to half orless.

Here, embodiments of the method may likewise be advantageous in whichthe inlet valve of the at least one inlet opening, after performing theadditional valve lift, is moved in the direction of the closed positionin order to reduce the valve lift by at least one third.

Embodiments of the method may also be advantageous in which the inletvalve of the at least one inlet opening, after performing the additionalvalve lift, is moved in the direction of the closed position in order toreduce the valve lift by at least one quarter.

In the above method variants, a valve lift curve with at least twomaxima is formed. That is to say that the inlet valve, when theadditional valve lift is reached, is not directly opened further inorder to perform the maximum valve lift for the purposes of a chargeexchange, but is initially moved in the direction of the closedposition. That is to say, the valve lift is initially reduced before afurther opening is initiated.

This approach may for example be necessary if the additional valve liftis performed very close to top dead center, in order to prevent contactbetween the piston and the inlet valve. It is then advantageous toreduce the valve lift before the inlet valve is opened further, orfully, during the course of the charge exchange.

Nevertheless, when the additional valve lift is reached, the inlet valvemay also be opened further directly, or with a delay, in order toperform the maximum valve lift for the purposes of a charge exchange.

Embodiments of the method may be advantageous in which an additionalvalve lift is performed which amounts to less than one quarter of themaximum valve lift.

Embodiments of the method may be advantageous in which an additionalvalve lift is performed which amounts to less than one sixth of themaximum valve lift.

Embodiments of the method may be advantageous in which an additionalvalve lift is performed which amounts to less than one eighth of themaximum valve lift.

The magnitude of the additional valve lift must basically be coordinatedwith the crank angle point at which the additional valve lift isperformed. The closer to top dead center the additional valve lift isperformed, the smaller the additional valve lift must be in order thatthe inlet valve does not come into contact with the piston during thecourse of the charge exchange. It may however be necessary to takenumerous other parameters into consideration, for example the pistonshape, the shape of the combustion chamber roof, but in particular thecompression ratio ε of the cylinder or of the internal combustionengine.

Embodiments of the method may be advantageous in which an additionalvalve lift of less than 2 mm is performed.

Embodiments of the method may be advantageous in which an additionalvalve lift of less than 1.5 mm is performed.

The specifications for the additional valve lift in the above methodvariants are merely exemplary, and are intended to illustrate therelationship with respect to the maximum valve lift, which may readilyamount to 8 mm to 12 mm.

Embodiments of the method may be advantageous in which a diesel engineis used as an internal combustion engine. As already stated, the methodaccording to the present application is particularly advantageous in thecase of internal combustion engines with a high compression ratio, forexample diesel engines, in which, to realize a valve overlap, the valvescannot be actuated and opened arbitrarily as desired, because the pistoncomes very close to the valves as it passes through top dead center. Inthe case of the method according to the present application, there is norisk of the piston coming into contact with an open inlet valve.

Embodiments of the method may be advantageous in which a superchargedinternal combustion engine is used as an internal combustion engine.

A pressure gradient between the intake system and exhaust-gas dischargesystem assists the scavenging of the cylinder with fresh air, that is tosay the scavenging process, such that it is advantageous to enable ahigh pressure in the intake system. The latter may be achieved by virtueof the internal combustion engine being supercharged. The chargepressure generated by supercharging, which at low engine speeds is oftenhigher than the exhaust-gas back pressure in the exhaust-gas dischargesystem, then prevails in the intake system.

The pressures in the intake system and in the exhaust-gas dischargesystem vary continuously owing to the intermittent charge exchange. Theevacuation of the combustion gases is, at the start of the chargeexchange, based on the high pressure difference between combustionchamber and exhaust-gas discharge system. This pressure-driven flowprocess is assisted by a high pressure peak. During the further courseof the charge exchange, the pressures in the combustion chamber and inthe exhaust-gas discharge system are equalized, and the combustion gasesare discharged as a result of the lift movement of the piston.Relatively large changes in pressure likewise occur at the inlet side.Consequently, the pressure difference between the intake system and theexhaust-gas discharge system, that is to say between the inlet openingand the outlet opening of the cylinder, also varies constantly.

In this context, embodiments of the method may be advantageous in whichan exhaust-gas-turbocharged engine is used as an internal combustionengine.

In the case of exhaust-gas-turbocharged internal combustion engines, thescavenging process has the special effect that the turbine, arranged inthe exhaust-gas discharge system, of an exhaust-gas turbocharger has agreater mass flow supplied to it. Said greater mass flow through theturbine leads to a higher charge pressure at the inlet side andultimately to an increase in torque.

The heating of the fresh air used for the scavenging process, and thescavenged residual gas, lead to an increase of the enthalpy of theexhaust-gas mass flow provided to the turbine, and thus likewise to anincrease in torque.

Embodiments of the method may be advantageous in which the outlet valveof the at least one outlet opening is actuated in such a way that saidoutlet valve performs an additional valve lift before the piston, duringthe course of the charge exchange, reaches bottom dead center and afterthe outlet valve, during the course of the charge exchange, hasperformed the maximum valve lift.

If, during the intake process of the charge exchange, in which thepiston moves downward, an outlet valve is opened before the pistonreaches bottom dead center, the at least one inlet valve is still open.The fresh air introduced into the cylinder via the inlet opening canthen flow through the cylinder, and exit the latter again via theoutlet, owing to the valve lift additionally being performed by theoutlet valve. The associated effects are, in part, the effects that havebeen described in conjunction with the additional valve lift of theinlet valve.

In the present case, scavenging of residual gas does not take place, ortakes place at most to a negligible extent, as a result of which theadvantages associated with residual gas scavenging, specifically thegeneration of a large cylinder fresh charge in the subsequent workingcycle and the increase in enthalpy owing to the scavenged residual gas,may be eliminated.

In the case of exhaust-gas-turbocharged internal combustion engines,however, the scavenging process has the same advantageous effect, albeitnot to the same extent. A greater mass flow is in turn provided to theturbine, arranged in the exhaust-gas discharge system, of an exhaust-gasturbocharger, whereby an increase in torque at constant engine speed isachieved. Said greater mass flow is however at a relatively lowtemperature, because the fresh air conducted through the cylinder isnot, or cannot be, heated either by scavenged residual gas or by apiston, which is situated close to bottom dead center.

Even though an additional valve lift at the inlet side offers greateradvantages than an additional valve lift at the outlet side, theimplementation of an additional outlet-side valve lift has the advantageof reducing the sensitivity of the method with respect to changes inexhaust-gas back pressure.

Furthermore, the lack of heating of the fresh air can advantageously beutilized for targeted cooling of the mass flow supplied to the turbine,that is to say to lower the turbine inlet temperature. In thisconnection, it must be taken into consideration that the operation of aninternal combustion engine is often, in particular at full load, limitedby the maximum admissible temperature at the turbine inlet.

In this respect, the present method variant, in which the outlet valveof the at least one outlet opening performs an additional valve lift,may also be implemented with the exclusive aim of cooling the mass flowsupplied to the turbine.

In the case of internal combustion engines in which each cylinder has atleast two inlet openings for the supply of fresh air via an intakesystem and at least two outlet openings for the discharge of the exhaustgases via an exhaust-gas discharge system, embodiments may beadvantageous wherein the inlet valves of at least two inlet openings areactuated in such a way that said inlet valves perform an additionalvalve lift.

In the case of internal combustion engines in which each cylinder has atleast two inlet openings for the supply of fresh air via an intakesystem and at least two outlet openings for the discharge of the exhaustgases via an exhaust-gas discharge system, embodiments may beadvantageous wherein the inlet valve of at least one inlet opening isactuated in such a way that said inlet valve performs an additionalvalve lift.

Turning to FIG. 1, a schematic diagram showing one cylinder ofmulti-cylinder engine 10, which may be included in a propulsion systemof a vehicle, is shown. Engine 10 may be controlled at least partiallyby a control system including controller 12 and by input from a vehicleoperator 132 via an input device 130. In this example, input device 130includes an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. A pedal position ofan accelerator pedal may be used to indicate a requested torque,Tq_(req), to controller 12 via pedal position sensor 134. Combustionchamber (e.g., cylinder) 30 of engine 10 may include combustion chamberwalls 32 with piston 36 positioned therein. Piston 36 may be coupled tocrankshaft 40 so that a reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 40 may be coupledto at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10. A drive wheel speed may indicate an available torque, Tq_(avail)from the engine 10. Furthermore, the drive wheel speed and theaccelerator pedal position sensor 134 may together indicate theavailable torque in relation to the requested torque.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

Fuel injector 66 is shown arranged in intake passage 42 in aconfiguration that provides what is known as port injection of fuel intothe intake port upstream of combustion chamber 30. Fuel injector 66 mayinject fuel in proportion to the pulse width of signal FPW received fromcontroller 12 via electronic driver 68. Fuel may be delivered to fuelinjector 66 by a fuel system (not shown) including a fuel tank, a fuelpump, and a fuel rail. In some embodiments, combustion chamber 30 mayalternatively or additionally include a fuel injector coupled directlyto combustion chamber 30 for injecting fuel directly therein, in amanner known as direct injection. In some cases, direct injection mayprovide increased cooling engine cylinders which can reduce knocking andallow for higher compression ratios and increased engine efficiency ascompared to operation without direct fuel injection.

Intake passage 42 may include a throttle 62 having a throttle plate 64.In this particular example, the position of throttle plate 64 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 62, a configuration that is commonlyreferred to as electronic throttle control (ETC). In this manner,throttle 62 may be operated to vary the intake air provided tocombustion chamber 30 among other engine cylinders. The position ofthrottle plate 64 may be provided to controller 12 by throttle positionsignal TP. Intake passage 42 may include a mass air flow sensor 120 anda manifold air pressure sensor 122 for providing respective signals MAFand MAP to controller 12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may be athree way catalyst (TWC), NOx trap, particulate filter, various otheremission control devices, or combinations thereof. As an example, anengine may be operated at an overall stoichiometric air-fuel ratio inorder to reduce NOx emissions. In some embodiments, during operation ofengine 10, emission control device 70 may be periodically reset byoperating at least one cylinder of the engine within a particularair/fuel ratio.

Full-volume exhaust gas sensor 76 is shown coupled to exhaust passage 48downstream of emission control device 70. Sensor 76 may be any suitablesensor for providing an indication of exhaust gas air/fuel ratio such asa linear oxygen sensor or UEGO (universal or wide-range exhaust gasoxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx,HC, or CO sensor. Further, a plurality of exhaust gas sensors may belocated at partial volume locations within the emission control devices.Other sensors 72 such as an air mass (AM) sensor, additional EGO sensor,and/or a temperature sensor may be disposed upstream of emission controldevice 70 to monitor the AM, oxygen content, and temperature,respectively, of the exhaust gas entering the emission control device.The sensor locations shown in FIG. 1 are just one example of variouspossible configurations. For example, the emission control system mayinclude a partial volume set-up with close coupled catalysts.

Compressor 14 draws air from air intake passage 42 to supply boostintake passage 42. Exhaust-gases spin turbine 16 which is coupled tocompressor 14 via shaft 17. In some examples, a charge or intake aircooler may also be provided (not shown). Compressor speed may beadjusted via adjusting a position of variable vane control or compressorbypass valve. In alternative examples, a waste gate 20 may replace or beused in addition to variable vane control. Variable vane control mayadjust a position of variable geometry vanes 19 of turbine 16.Exhaust-gases can pass through turbine 16 supplying little energy torotate turbine 16 when vanes 19 are in an open position. Exhaust-gasescan pass through turbine 16 and impart increased force on turbine 16when vanes 19 are in a closed position. Alternatively, waste gate 20allows exhaust-gases to flow around turbine 16 so as to reduce theamount of energy supplied to the turbine 16. Furthermore, turbine 16 maybe a turbine with fixed geometry. A compressor bypass valve (not shown)may allow compressed air at the outlet of compressor 14 to be returnedto the input of compressor 14. In this way, the efficiency of compressor14 may be reduced so as to affect the flow of compressor 14 and reducethe possibility of compressor surge. In this way, the engine maycomprise a turbocharged engine. In other examples, the engine maycomprise a supercharged engine, wherein a supercharger compressor 14 isused to compress the intake air, but the compressor is not coupled to ashaft and is not driven by an exhaust turbine. Power for a superchargercompressor can be provided mechanically by a belt, gear, shaft, or chainconnected to the engine's crankshaft, for example.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; AM and/or temperature of the exhaust gas entering thecatalyst from sensor 72; exhaust gas air to fuel ratio from sensor 76;and absolute manifold pressure signal, MAP, from sensor 122. Enginespeed signal, RPM, may be generated by controller 12 from signal PIP.Manifold pressure signal MAP from a manifold pressure sensor may be usedto provide an indication of vacuum, or pressure, in the intake manifold.Note that various combinations of the above sensors may be used, such asa MAF sensor without a MAP sensor, or vice versa. During stoichiometricoperation, the MAP sensor can give an indication of engine torque (e.g.,available torque). Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses for each revolution of the crankshaft. Additionally,controller 12 may communicate with a cluster display device 136, forexample to alert the driver of faults in the engine or exhaustafter-treatment system.

Storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by processor 102 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

Each combustion chamber (e.g., cylinder) 30 may be serviced by one ormore valves. In the present example, each cylinder 30 includes acorresponding intake valve 52 and an exhaust valve 54. Engine 10 furtherincludes one or more camshafts 65 for operating intake valve 52 and/orexhaust valve 54. In the depicted example, intake camshaft 65 is coupledto intake valve 52 and can be actuated to operate intake valve 52. Insome embodiments, where the intake valve of a plurality of cylinders 30are coupled to a common intake camshaft, the common intake camshaft canbe actuated to operate the intake valves of all the coupled cylinders.

Intake valve 52 is actuatable between an open position that allowsintake air into the corresponding cylinder and a closed positionsubstantially blocking intake air from the cylinder. Intake camshaft 65may be included in intake valve actuation system 69. Intake camshaft 65includes intake cam 67 which has a cam lobe profile for opening intakevalve 52 for a defined intake duration. In some embodiments (not shown),the camshaft may include additional intake cams with an alternate camlobe profile that allows the intake valve 52 to be opened for analternate duration (herein also referred to as a cam profile switchingsystem). Based on the lobe profile of the additional cam, the alternateduration may be longer or shorter than the defined intake duration ofintake cam 67. The lobe profile may affect cam lift height, camduration, and/or cam timing. A controller may be able to switch theintake valve duration by moving intake camshaft 65 longitudinally andswitching between cam profiles.

In the same manner, each exhaust valve 54 is actuatable between an openposition allowing exhaust gas out of the corresponding cylinder and aclosed position substantially retaining gas within the cylinder. It willbe appreciated that while only intake valve 52 is shown to becam-actuated, exhaust valve 54 may also be actuated by a similar exhaustcamshaft (not shown). In some embodiments, where the exhaust valve of aplurality of cylinders 30 is coupled to a common camshaft, the exhaustcamshaft can be actuated to operate the exhaust valves of all thecoupled cylinders. As with intake camshaft 65, when included, theexhaust camshaft may include an exhaust cam having a cam lobe profilefor opening exhaust valve 54 for a defined exhaust duration. In someembodiments, the exhaust camshaft may further include additional exhaustcams with an alternate cam lobe profile that allows exhaust valve 54 tobe opened for an alternate duration. The lobe profile may affect camlift height, cam duration, and/or cam timing. A controller may be ableto switch the exhaust valve duration by moving the exhaust camshaftlongitudinally and switching between cam profiles.

It will be appreciated that the intake and/or exhaust camshafts may becoupled to cylinder subsets, and multiple intake and/or exhaustcamshafts may be present. For example, a first intake camshaft may becoupled to the intake valves of a first subset of cylinders while asecond intake camshaft may be coupled to the intake valves of a secondsubset of cylinders. Likewise, a first exhaust camshaft may be coupledto the exhaust valves of a first subset of cylinders while a secondexhaust camshaft may be coupled to the exhaust valves of a second subsetof cylinders. Further still, one or more intake valves and exhaustvalves may be coupled to each camshaft. The subset of cylinders coupledto the camshaft may be based on their position along an engine block,their firing order, the engine configuration, etc.

Intake valve actuation system 69 and exhaust valve actuation system (notshown) may further include push rods, rocker arms, tappets, etc. Suchdevices and features may control actuation of the intake valve 52 andthe exhaust valve 54 by converting rotational motion of the cams intotranslational motion of the valves. As previously discussed, the valvescan also be actuated via additional cam lobe profiles on the camshafts,where the cam lobe profiles between the different valves may providevarying cam lift height, cam duration, and/or cam timing. However,alternative camshaft (overhead and/or pushrod) arrangements could beused, if desired. Further, in some examples, cylinders 30 may each havemore than one exhaust valve and/or intake valve. In still otherexamples, each of the exhaust valve 54 and intake valve 52 of one ormore cylinders may be actuated by a common camshaft. Further still, insome examples, some of the intake valves 52 and/or exhaust valves 54 maybe actuated by their own independent camshaft or other device.

Engine 10 may include variable valve timing (VVT) systems, for example,variable cam timing (VCT) system 80. A variable valve timing system maybe configured to open an intake valve for a first duration and anexhaust valve for a second duration. In one example, the system may beconfigured to perform an additional intake and/or exhaust valve liftbased on engine operating conditions such as engine speed and exhaustair mass flow temperature.

VCT system 80 may be configured to advance or retard valve timing byadvancing or retarding cam timing and may be controlled by controller12. VCT system 80 may be configured to vary the timing of valve openingand closing events by varying the relationship between the crankshaftposition and the camshaft position. For example, VCT system 80 may beconfigured to rotate intake camshaft 65 independently of the crankshaftto cause the valve timing to be advanced or retarded.

The valve/cam control devices and systems described above may behydraulically powered, or electrically actuated, or combinationsthereof. In one example, a position of the camshaft may be changed viacam phase adjustment of an electrical actuator (e.g., an electricallyactuated cam phaser) with a fidelity that exceeds that of mosthydraulically operated cam phasers. Signal lines can send controlsignals to and receive a cam timing and/or cam selection measurementfrom VCT system 80.

By adjusting VCT system 80, a position of intake camshaft 65 can beadjusted to thereby vary an opening and/or closing timing of intakevalve 52. As such, by varying the opening and closing of intake valve52, an amount of positive valve overlap between intake valve 52 andexhaust valve 54 can be varied. For example, VCT system 80 may beadjusted to advance or retard an opening and/or a closing of intakevalve 52 relative to a piston position. VCT system 80 may also comprisea cam position sensor for detecting the position of a cam. The camposition sensor may also determine the rate of change of the camposition, from which the direction of the cam movement may bedetermined. For example, the cam position sensor may determine if a camis moving towards a new cam position (e.g., away from the default pinnedposition), or towards the default pinned position (e.g., away from thenew cam position. Furthermore, the cam position sensor may be able todetect the position of multiple cams so that a degree of camsynchronization between multiple cams can be determined. For example, bymeasuring instantaneous cam positions and/or rates of change of campositions, the cam position sensor can determine the degree ofsynchronization between multiple cams.

During engine operation, a cylinder piston gradually moves downward fromTDC, bottoming out at BDC by the end of the power stroke. The pistonthen returns to the top, at TDC, by the end of the exhaust stroke. Thepiston then again moves back down, towards BDC, during the intakestroke, returning to its original top position at TDC by the end of thecompression stroke. During cylinder combustion, an exhaust valve may beopened just as the piston bottoms out at the end of the power stroke.The exhaust valve may then close as the piston completes the exhauststroke, remaining open at least until a subsequent intake stroke hascommenced. In the same way, an intake valve may be opened at or beforethe start of an intake stroke, and may remain open at least until asubsequent compression stroke has commenced.

The valves may be operated with positive valve overlap wherein for ashort duration before the end of the exhaust stroke and after thecommencement of the intake stroke, both intake and exhaust valves may beopen. This period, during which both valves may be open, is referred toas a positive (intake to exhaust) valve overlap. As elaborated herein,the VCT system 80 may be adjusted so that an amount of positive valveoverlap during selected engine operating conditions is increased. In oneexample, valve positive overlap may occur as a result of additionalvalve lift(s). An extra intake valve lift just before the gas exchangetop-dead center results in a positive valve overlap and a positivepressure gradient. Likewise, an extra exhaust valve lift just before thepiston bottom-dead center during the intake stroke results in positivevalve overlap and positive pressure gradient. These extra valve eventsmust be switchable (on/off).

FIG. 1 also shows a controller 12, which may be any electronic controlsystem of the vehicle in which engine 10 is installed. In embodimentswhere at least one intake or exhaust valve is configured to open andclose according to an adjustable timing, the adjustable timing and/orthe additional valve lifts may be controlled via the electronic controlsystem to regulate an amount of exhaust present in a combustion chamberduring ignition. For example, positive valve overlap may be increased inorder to scavenge combusted exhaust gases from the engine cylinders.

The electronic control system may also be configured to command theopening, closure and/or adjustment of various other electronicallyactuated valves in the engine 10 as needed to enact any of the controlfunctions described herein. These valves may include throttle valves,compressor by-pass valves, waste gates, EGR valves and shut-off valves,various reservoir intake and exhaust valves, for example. The controllermay also adjust the amount of fuel, as well as injection timing, of thefuel injectors. As such, the controller may adjust the VCT system and anair-fuel ratio. Further, to assess operating conditions in connectionwith the control functions of the engine 10, the controller may beoperatively coupled to a plurality of sensors arranged throughout theengine 10. These may include flow sensors, temperature sensors,pedal-position sensors, pressure sensors, a mass air flow sensor, etc.Specifically, a pedal position sensor 134 is shown coupled to anaccelerator pedal 130 for sensing force applied by vehicle operator 132.The controller 12 may use data from these various sensors to estimateother engine operating conditions.

FIG. 2A shows, in a diagram, the valve lift curves h_(intake),h_(exhaust) of an inlet valve and of an outlet valve in accordance witha first embodiment of the method. Also illustrated is the pressuredifference Δp between the intake system and the exhaust-gas dischargesystem, that is to say between the inlet side and the outlet side.

During the charge exchange, the exhaust gas may be evacuated from thecylinder by virtue of the outlet valve being opened and performing themaximum valve lift Δh_(max,exhaust). The inlet valve is consequentlyopened in order to fill the cylinder with fresh air again, wherein theinlet valve performs the maximum valve lift Δh_(max,intake) during thecourse of the charge exchange.

The inlet valve is in this case actuated such that said inlet valveperforms an additional valve lift Δh_(add,intake), specifically beforethe inlet valve performs the maximum valve lift Δh_(max,intake) duringthe course of the charge exchange and before the piston reaches top deadcenter during the course of the charge exchange. Consequently, the inletvalve performs two valve lifts Δh_(max,intake), Δh_(add,intake), whereinthe actual, relatively large valve lift Δh_(max,intake), which servesprimarily for the charge exchange, may be preceded by an additional,relatively small valve lift Δh_(add,intake). The additional, relativelysmall valve lift Δh_(add,intake) serves for the scavenging of residualgas out of the cylinder. The scavenging of residual gas may be assistedby the piston moving toward top dead center, whereby the combustionchamber volume may be reduced in size. A positive pressure gradient Δpbetween the intake system and exhaust-gas discharge system additionallyassists the scavenging process with fresh air. As great a cylinder freshcharge as possible in the next working cycle better enables an increasein power and an increase in torque at an unchanged engine speed.

In the case of exhaust-gas-turbocharged internal combustion engines, thescavenging process has the effect that the turbine arranged in theexhaust-gas discharge system may be provided with a greater mass flow,whereby a higher charge pressure can be generated at the inlet side. Thehigher charge pressure likewise leads to an increase in torque at aconstant engine speed. The hot scavenged residual gas increases theenthalpy of the mass flow supplied to the turbine, which may beadditionally increased yet further by virtue of the fresh air that isconducted through the cylinder during the course of the scavenging ofresidual gas being heated by convection as it flows through thecylinder.

In the present case, the inlet valve, after performing the additionalvalve lift Δh_(add,intake), may not be moved back into the closedposition but may be opened further for the purpose of performing themaximum valve lift Δh_(max,intake) during the course of the chargeexchange. However, the inlet valve, after performing the additionalvalve lift Δh_(add,intake), may be initially moved in the direction ofthe closed position, in order to reduce the valve lift approximately byhalf, before said inlet valve is opened further for the purpose ofperforming the maximum valve lift Δh_(max,intake). The valve lift curvethus formed has two maxima.

In the first method variant as per FIG. 2A, the outlet valve may beactuated in such a way that said outlet valve likewise performs anadditional valve lift Δh_(add,exhaust).

The outlet valve may be opened again after the outlet valve hasperformed the maximum valve lift Δh_(max,exhaust) during the course ofthe charge exchange and before the piston reaches bottom dead centerduring the course of the intake process.

While the outlet valve performs the additional valve liftΔh_(add,exhaust), the inlet valve remains open. The fresh air introducedinto the cylinder via the inlet opening can exit the cylinder again viathe outlet. A positive pressure gradient Δp between the intake systemand exhaust-gas discharge system assists the flow through the cylinder.The additional valve lift Δh_(add,exhaust) of the outlet valve servesless for the scavenging of residual gas and more for the cooling of themass flow supplied to the turbine, that is to say for lowering theturbine inlet temperature. Specifically, the fresh air conducted throughthe cylinder may not be heated either by scavenged residual gas or by apiston, which is situated adjacent to bottom dead center. A coolingeffect can be achieved owing to the lack of heating of the fresh air asit flows through the cylinder.

The additional valve lift Δh_(add,exhaust) of the outlet valve isfurthermore also suitable, albeit not to the same extent, for increasingthe mass flow supplied to the turbine and thus for increasing torque ata constant engine speed, although this increased mass flow may be at alower temperature. In this respect, an outlet-side additional valve liftΔh_(add,exhaust) assists the inlet-side additional valve liftΔh_(add,intake).

FIG. 2B shows, in a diagram, the valve lift curves h_(intake),h_(exhaust) of an inlet valve and of an outlet valve in accordance witha second embodiment of the method. The pressure difference Δp betweenthe intake system and the exhaust-gas discharge system is likewiseillustrated.

It is sought to explain only the differences in relation to the methodvariant illustrated in FIG. 2A, for which reason reference is otherwisemade to FIG. 2A. The same reference signs are used.

By contrast to the method variant illustrated in FIG. 2A, it is the casein the method variant illustrated in FIG. 2B that an additional valvelift Δh_(add,exhaust) of the outlet valve may be omitted.

An additional valve lift Δh_(add,exhaust) of the outlet valve may not beused either for increasing the mass flow supplied to the turbine for thepurposes of increasing torque or for cooling said mass flow for thepurposes of lowering the turbine inlet temperature.

Turning now to FIG. 3, an example method flowchart 300 for actuating theadditional valve lifts its shown. The method may include actuatingdevice 69 from FIG. 1, for example.

At 310, the method may include opening exhaust valve(s) to max valvelift Δh_(max,exhaust) during charge exchange of a combustion chamber(combustion chamber 30 from FIG. 1, for example). In one example, theexhaust valve is opened to a maximum valve lift during the exhauststroke wherein the piston (such as piston 36 from FIG. 1, for example)moves toward TDC.

At 312, the method may include actuating an intake valve or intakevalves open before the piston reaches TDC during the charge exchange toperform an additional valve lift such that intake system pressure isgreater than exhaust-gas discharge system pressure. For example, theintake valve may be actuated to open after the maximum exhaust valvelift but before the exhaust valve closes during the exhaust stroke andbefore the maximum intake valve lift. In one example the additionalvalve lift may be performed up until 50° CA before TDC. In anotherexample, the additional valve lift may be performed up until 30° CAbefore TDC. In this way, both an exhaust valve and intake valve areopen, resulting in a positive valve overlap. Further, the additionalintake valve lift may occur such that there is a positive pressuregradient during the course of the additional valve lift. A return to anegative pressure gradient marks the intake valve closing or movingtowards closing before opening to maximum intake valve lift. Further,the pressure curve of FIGS. 2A and 2B, for example, may vary uponoperating conditions so that the timing and occurrences of theadditional valve lifts may also vary. However, the additional valvelifts still occur during the engine strokes as portrayed such that theintake system pressure is greater than exhaust system pressure. Theintake valve may be actuated by a valve drive, such as valve actuationsystem 69 from FIG. 1, for example. The additional valve lift may beless than 2 mm, or less 1.5 mm.

At 314, the method may include opening inlet valve(s) to maximum valvelift Δh_(max,intake) during the course of charge exchange. In oneexample, the maximum valve lift may occur during the intake stroke, suchthat the piston is moving from TDC to BDC.

At 316, the method may include actuating an exhaust valve or exhaustvalves to open before piston reaches BDC to perform an additionalexhaust valve lift such that intake pressure is greater than exhaustpressure. For example, the exhaust valve may be actuated to open at orafter the intake valve has reached a maximum valve lift and closesbefore the piston reaches BDC such that an intake and exhaust valve areopen simultaneously. Furthermore, the opening and closing of theadditional exhaust valve lift, like the additional intake valve lift,corresponds to a positive pressure gradient such that intake pressure isgreater than exhaust pressure. The method may then end.

Turning now to FIG. 4, an example operating routine 400 is shown. Thisroutine may be performed by a controller, such as controller 20 fromFIG. 1, in order that additional valve lifts occur according to themethod of FIG. 3, for example.

At 410, the method may include estimating and/or measuring vehicleoperating conditions. For example, engine speed, engine load, turbineinlet temperature, mass air flow, variable valve timing, crank angle,etc. may be estimated and/or measured by the various sensors shown inFIG. 1, for example.

At 412, the method may determine whether engine speed, e.g. RPM, isbelow a threshold. In one example, the threshold may be 2500 RPM, and aspeed range under 2500 RPM may be a low speed range wherein at certaintime frames of the engine cycle, the pressure at the intake valve ishigher than the pressure at the exhaust valve.

If yes, the method may switch additional intake valve lift ON, forexample, by a switchable roller finger follower. When ON, the controllermay send instructions stored in non-transitory memory to signal theactuation of the intake valve to perform an additional valve liftaccording to the method steps displayed from 310 to 312 of FIG. 3, forexample.

If no, the method may switch additional intake valve lift OFF andproceed to 420.

At 420, the method may determine if turbine inlet temperature is greaterthan a threshold temperature. The temperature may be determined by atemperature sensor for example.

If yes, the method may switch the additional exhaust valve lift ON at424. When ON, the controller may send instructions stored innon-transitory memory to signal the actuation of the exhaust valve toperform an additional valve lift according to the method steps 314 and316 of FIG. 3, for example. In this way, fresh air is blown through thecylinder, but is not being heated by residual gas or the hot piston asthe piston is at BDC. Some engines, such as diesel engines, may belimited by exhaust gas temperature at full load. An additional exhaustvalve lift may control exhaust temperature and may provide a coolingeffect to counteract the increase in exhaust temperature that may becaused by the additional intake valve lift if desired. The method maythen end.

If no, the method at 422 may switch the additional exhaust valve OFF andend.

In this way, the method provides for switchable extra valve lifts whichmay increase low end torque with and/or without temperature increase toincrease power and reduce scavenging losses.

Note that a cylinder cycle may be repeatedly performed in each cylinder,a single cylinder cycle including in one example intake, compression,combustion/expansion, and exhaust strokes. Note that the example controland estimation routines included herein can be used with various engineand/or vehicle system configurations. The control methods and routinesdisclosed herein may be stored as executable instructions innon-transitory memory. The specific routines described herein mayrepresent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various actions, operations, and/or functions illustratedmay be performed in the sequence illustrated, in parallel, or in somecases omitted. Likewise, the order of processing is not necessarilyrequired to achieve the features and advantages of the exampleembodiments described herein, but is provided for ease of illustrationand description. One or more of the illustrated actions, operationsand/or functions may be repeatedly performed depending on the particularstrategy being used. Further, the described actions, operations and/orfunctions may graphically represent code to be programmed intonon-transitory memory of the computer readable storage medium in theengine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

REFERENCE SYMBOLS

-   -   h_(exhaust) Valve lift of an outlet valve    -   h_(intake) Valve lift of an inlet valve    -   Δh Valve lift    -   Δh_(max,exhaust) Maximum valve lift of an outlet valve    -   Δh_(max,intake) Maximum valve lift of an inlet valve    -   Δh_(add,exhaust) Additional valve lift of an outlet valve    -   Δh_(add,intake) Additional valve lift of an inlet valve    -   Δp Pressure difference between intake system and exhaust-gas        discharge system    -   ° CA Degrees crank angle

1. A system for performing a charge exchange in an internal combustionengine comprising: at least one cylinder head with at least onecylinder, each cylinder having at least one inlet opening for the supplyof fresh air via an intake system and having at least one outlet openingfor discharging the exhaust gases via an exhaust-gas discharge systemand having a piston which is movable along a piston longitudinal axisbetween a bottom dead center and a top dead center, and at least twovalve drives with at least two valves which are movable along theirlongitudinal axis between a valve closed position and a valve openposition, performing a maximum valve lift, in order to open up and blockthe at least one inlet opening and the at least one outlet opening ofthe at least one cylinder during the course of a charge exchange, andhaving at least two actuating devices for opening the valves counter toa preload force, wherein the inlet valve of the at least one inletopening is actuated to perform an additional valve lift before thepiston, during the course of the charge exchange, reaches top deadcenter and before the inlet valve, during the course of the chargeexchange, performs the maximum valve lift, and the outlet valve of theat least one outlet opening is actuated to perform an additional valvelift before the piston, during the course of the charge exchange,reaches bottom dead center and after the outlet valve, during the courseof the charge exchange, has performed the maximum valve lift.
 2. Thesystem of claim 1, wherein the inlet valve of the at least one inletopening is actuated, for the purpose of performing the additional valvelift, while at least one outlet opening of the at least one cylinder isat least temporarily open.
 3. The system of claim 1, wherein the inletvalve of the at least one inlet opening is actuated, for the purpose ofperforming the additional valve lift, only when a pressure gradientprevails which is such that the pressure in the intake system is higherthan the pressure in the exhaust-gas discharge system.
 4. The system ofclaim 1, wherein the additional valve lift of the inlet valve isperformed up until 50° CA before top dead center.
 5. The system of claim1, wherein the additional valve lift of the inlet valve is performed upuntil 30° CA before top dead center.
 6. The system of claim 1, whereinthe inlet valve of the at least one inlet opening is, after performingthe additional valve lift, moved into the closed position again beforesaid inlet valve is opened again for the purpose of performing themaximum valve lift during the course of the charge exchange.
 7. Thesystem of claim 1, wherein the inlet valve of the at least one inletopening, after performing the additional valve lift, is not moved intothe closed position but is opened further for the purpose of performingthe maximum valve lift during the course of the charge exchange.
 8. Thesystem of claim 7, wherein the inlet valve of the at least one inletopening, after performing the additional valve lift, is moved in thedirection of the closed position in order to reduce the valve lift by upto half or less.
 9. The system of claim 7, wherein the inlet valve ofthe at least one inlet opening, after performing the additional valvelift, is moved in the direction of the closed position in order toreduce the valve lift by at least one third.
 10. The system of claim 7,wherein the inlet valve of the at least one inlet opening, afterperforming the additional valve lift, is moved in the direction of theclosed position in order to reduce the valve lift by at least onequarter.
 11. The system of claim 1, wherein an additional valve lift isperformed which amounts to less than one quarter of the maximum valvelift.
 12. The system of claim 1, wherein an additional valve lift isperformed which amounts to less than one sixth of the maximum valvelift.
 13. The system of claim 1, wherein an additional valve lift ofless than 2 mm is performed.
 14. The system of claim 1, wherein anadditional valve lift of less than 1.5 mm is performed.
 15. A method foran engine comprising: opening at least one exhaust valve to maximumvalve lift during a charge exchange of a combustion chamber comprising apiston; actuating at least one intake valve before the piston reachestop dead center of the combustion chamber during the charge exchange toperform an additional intake valve lift in response to an intakepressure being greater than an exhaust pressure; opening at least oneinlet valve to maximum valve lift during charge exchange; actuating atleast one exhaust valve before the piston reaches bottom dead centerduring charge exchange to perform an additional exhaust valve lift inresponse to the intake system pressure being greater than the exhaustsystem pressure.
 16. A method comprising: performing combustion in acylinder wherein each an inlet and exhaust valve of the cylinder performmore than one valve lift in response to a positive pressure gradientbetween an intake system and an exhaust system.
 17. The method of claim16, wherein the inlet valve is actuated to perform an additional valvelift before the piston reaches top dead center during charge exchangeand before the inlet valve performs a maximum valve lift in the cylindercycle.
 18. The method of claim 17, wherein the outlet valve is actuatedto perform an additional valve lift before the piston, during the chargeexchange, reaches bottom dead center and after the outlet valve, duringthe charge exchange, has performed a maximum valve lift.
 19. The methodof claim 16, wherein the engine is spark ignited and turbocharged withdirect fuel injection.
 20. The method of claim 16, wherein the positivepressure gradient is in response to an intake system pressure beinggreater than an exhaust system pressure.